1. Field of the Invention
The present invention concerns the field of signaling devices adapted to use in remote control applications, and in particular relates to an infra-red transmitter and receiver that have outstanding range and immunity to interference.
2. Description of Related Art
Communication links for remote control applications have used a number of different technologies to transmit the remote control signals. At one time, actual physical connections, as through electrical wire, were a common means of implementing remote control. Other direct physical links capable of transmitting data have also been used, including pneumatic lines, hydraulic lines, and optical data fibers. However, most remote control applications operate without a direct physical link between the controller and the device to be controlled. Some type of signal transmission not requiring a physical connection is used instead.
Essentially, signal transmission without physical connection is limited to acoustic or electromagnetic radiation (radiant energy). Acoustic systems generally have poor range and are limited to direct line of sight applications. While sound waves can readily be reflected around comers, most small portable transmitters do not generate sufficiently strong outputs to make such reflection feasible. In the electromagnetic spectrum, signal transmission is a characteristic of the particular frequency. At longer wavelengths (so-called radio waves), the signals can pass through material objects and can have very good range. A significant problem can be interference from the plethora of naturally occurring radio wave sources. However, the present inventor has previously designed an electromagnetic system particularly advantageous to use with radio waves, but can be used with any radiant energy, that overcomes many of the problems inherent with electromagnetic radiation at these frequencies. This system is described in U.S. Pat. No. 4,482,895, which is incorporated herein by reference.
In spite of these advances made with radio wave communication links, a more advantageous method of performing remote control is through the use of digitally encoded optical signals. Generally, these optical signals are generated by light emitting diodes (LED) in a small hand-held remote controller. These transmissions are generally limited to infra-red (IR) wavelengths in order to make them invisible to humans. This produces a small, inexpensive remote control system that is generally immune to any interference or spurious signals. These remote controllers are advantageously employed in any of a large number of consumer electronic devices, such as televisions, VCRs, stereos and even home security systems. This same technology is also widely employed to synchronize separate devices, such as in "slave" photographic flashes. A general limitation of this technology is that it is limited to line of sight applications indoors. While IR can be reflected around comers similar to acoustic energy, small hand-held transmitters are generally incapable of producing sufficiently bright IR beams to take advantage of such reflection. Further, the IR beams are generally too weak to effectively compete with sunlight in outdoor applications.
Therefore, there remains a significant need for a remote control technology with the freedom from interference of the current IR system while providing extended range including outdoor operation. Besides the current uses of IR remote controllers, such an improved technology would also be applicable to certain new uses. In particular, such a technology would be ideal for remote detonation of explosives, as in construction and ordinance demolition. Currently, these remote control functions are carried out with radio wave-based devices, which unsatisfactory pose the significant danger that random interference will cause an inadvertent explosion. While it is possible to apply elaborate encryption technologies to radio wave-based remote detonators, this adds considerable complexity and cost to the receiver which is necessarily a disposable unit that does not survive the explosion that it initiates.
As will be explained below, the present inventor has adopted a solution to the countervailing demands of remote control devices that depends on pulse coded optical energy produced by a gas discharge tube. A properly modulated gas discharge tube, such as a xenon flash tube, can produce an extremely bright output with relatively modest power input. Further, a significant percentage of such radiation is in the infra-red wavelength, so that the pulsed optical signal is essentially invisible with proper filtering. This pulsed optical radiation can be used outdoors to provide line of sight remote control over a distance of many miles if properly columnated. Indoors, the extraordinary intensity of the signal allows it to be efficiently reflected by walls and other surfaces allowing remote control around at least four light blind comers.